The present invention relates to a ligand of inositol-1,4,5-trisphosphate receptor.
D-Myo-inositol-1,4,5-trisphosphate (herein occasionally abbreviated as xe2x80x9cIP3xe2x80x9d) is a second messenger that binds to the IP3 receptor to cause release of Ca2+ from the Ca2+ storage sites in cells, and it controls kinetics of intracellular Ca2+ concentration in variety of cells. IP3 plays an important role for control of various cellular functions such as secretion, insemination, muscular contraction, nervous signal transmission and cellular growth (Berridge, M. J., Nature, 361, 315, 1993; Clapham, D. E., Cell, 80, 259, 1995).
In order to study the signal transmission induced by IP3, a lot of IP3 analogues have been synthesized (Li, W., et al., Nature, 392, 936, 1998; McCarren, M. et al., J. Neuron, 3, 461, 1989), and the structures of the IP3 receptors and other IP3 binding proteins have been examined (Mourey, R. J. et al., Biochemistry, 32, 1719, 1993). It has been reported that, even though the phosphate in the 1-position of IP3 is modified, its binding affinity to the IP3 receptor is not substantially affected (Schafer, R., et al., Biochem. J., 272, 817, 1990; Prestwich, G. D. et al., J. Am. Chem. Soc., 113, 1822, 1991). It is known that adenophostins, metabolites isolated from a culture of Penicillium brevicompactum, are most potent agonists to the IP3 receptors (Takahashi, M., et al., J. Biol. Chem., 269, 369, 1994).
The inventors of the present invention conducted various studies to provide a novel IP3 receptor ligand. As a result, they unexpectedly found that compounds having extremely high affinity to the IP3 receptor can be provided by modifying the phosphate in the 1-position of IP3 with a dye derivative or a fluorescent dye derivative such as malachite green and fluorescein. The present invention was achieved on the basis of the above findings.
The present invention thus provides compounds represented by the following general formula (I) or salts thereof: 
wherein R represents a group represented by the following formula (A), (B) or (C): 
wherein R1 and R2 independently represent a C1-6 alkyl group; R3 represents an amino group, a mono(C1-6 alkyl)amino group, a di(C1-6 alkyl)amino group, or a C1-6 alkoxy group; and X- represents an anion, and n represents an integer of 2 to 5.
According to preferred embodiments of the present invention, provided are the aforementioned compounds or salts thereof, wherein the compounds represented by the general formula (I) are those represented by the following formula (I-1): 
wherein R has the same meaning as that defined above; the aforementioned compounds or salts thereof, wherein R is a group represented by the formula (A) wherein R1 and R2 represent a methyl group, R3 represents a dimethylamino group, and X- represents a chlorine ion, and n is 3; and the aforementioned compounds or salts thereof, wherein R is a group represented by the formula (A) wherein R1 and R2 represent a methyl group, R3 represents a dimethylamino group and X- represents a chlorine ion, and n is 3.
From another aspect of the present invention, there are provided IP3 receptor ligands which comprises a compound represented by the aforementioned general formula (I) or a salt thereof. IP3 receptor can be denatured by binding the aforementioned IP3 receptor ligand and then irradiating with light. Therefore, the IP3 receptor ligands comprising the compound represented by the aforementioned general formula (I) or a salt thereof are useful as regents for denaturing the IP3 receptor. The present invention also provides medicaments comprising the compound represented by the aforementioned general formula (I) or a salt thereof. These medicaments are useful as agents for prophylactic and/or therapeutic treatment of diseases resulting from supernumerary IP3 or hyper-expression of the IP3 receptor.
From still further aspect of the present invention, there are provided methods for denaturing the IP3 receptor, which comprise the steps of binding the compound represented by the aforementioned general formula (I) or a salt thereof to the IP3 receptor and then irradiating the result with light. The present invention also provides cells or cell extracts, of which IP3 receptor is denatured, preferably by the aforementioned methods.